For a spindle motor used in a signal recording and reproducing device such as a hard disk drive, various fluid dynamic pressure bearings have conventionally been used. The fluid dynamic pressure bearing is a bearing in which a lubricating liquid such as oil is interposed between a shaft body and a sleeve and a fluid pressure generated in the lubricating liquid is used as a supporting force.
One example of a spindle motor using a conventional dynamic pressure bearing is illustrated in FIG. 13. In this spindle motor, a pair of radial dynamic pressure bearing mechanism 137, 137 are arranged away from each other in an axial direction between an outer peripheral surface of a shaft body 131 formed integrally with a rotor 105 and an inner peripheral surface of a sleeve 133 into which the shaft body 131 is inserted rotatably. In addition, a pair of thrust bearing mechanism 136, 136 are Conned between an upper surface of a disk-shaped thrust plate 134 protruded from an outer peripheral surface of one end part of the shaft body 131 outward in a radial direction and a step formed in the sleeve 133, and between a lower surface of the thrust plate 134 and a thrust bush 132 closing one opening of the sleeve 133, respectively. Above the radial dynamic pressure bearing mechanism, a tapered seal part 140 is formed into peripheral surface of the shaft body 131.
With respect to such a spindle motor, further reduction in thickness has been sought after. It is because demand for compact information equipment has been increased, and according to this, miniaturization and reduction in thickness have also been sought after with respect to a hard disk drive or the like.
However, in the case where the spindle motor as shown in FIG. 13 is made thin, the height of a fluid dynamic pressure bearing device is inevitably imposed strict limitation on. Therefore, a span between to two radial dynamic pressure bearing mechanisms cannot help being reduced. This, in particular, reduces resistance to an external force trying to collapse the shaft body (rigidity), thereby making the design of bearing extremely difficult. A thin fluid dynamic pressure bearing device with strong bearing rigidity or a thin spindle motor with excellent performance has been sought after.